Asymmetric alternating prism arrays

ABSTRACT

A luminaire is provided which includes a light source, a light guide that receives light radiating from the light source, and a plurality of prisms adjacent the light guide that redirect the light from the light guide substantially perpendicular to a longitudinal axis of the light guide. The prism angles, in one embodiment, are 25°−90°−65°. The fine pitch prism arrays preferably alternate or flip-flop every few millimeters, for example, one to two millimeters to create the visual appearance of bright and dark bands which cause the structure to appear like macro prisms.

RELATED APPLICATIONS

[0001] This application is a divisional of U.S. application Ser. No. 09/726,239, filed on Nov. 29, 2000, which claims the benefit of U.S. application Ser. No. 60/208,339, filed May 31, 2000, and U.S. application Ser. No. 60/168,586, filed on Dec. 2, 1999, the entire teachings of the above applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] Luminaires typically include a lighting source, a waveguide, and microprisms used to redirect the light in a desired direction. These luminaires are used to provide a more uniform light distribution than conventional light systems and alleviate glare in applications such as office space, boardrooms, and customer service centers.

SUMMARY OF THE INVENTION

[0003] A luminaire is provided which includes a light source, a light guide that receives light radiating from the light source, and a plurality of tilted prism arrays for redirecting the light in a first direction. In one embodiment, the plurality of prism arrays, which can include linear prisms, periodically alternate orientation along the light guide. The linear prisms can have included angles of 25, 90, and 65 degrees. The prism arrays can alternate or flip-flop in orientation every few millimeters, for example, one to two millimeters. A tilted prism can have sides on each side of the peak with a first length from the valley to the peak on one side and a second length from the valley to the peak on a second side of the prism, where the first length is different in length from the second length, thereby tilting or canting the prisms. The tilting angle of the prisms is between the optical axis and a line perpendicular to the window side. The tilting angle can be in the range between about 20 and 70 degrees.

[0004] The prism arrays can include peaks and valleys along a first axis. The prism arrays can also include peaks and valleys along a second axis different than the first axis, such as substantially perpendicular or offset about 60 degrees relative to the first axis. The prism arrays can further include peaks and valleys along a third axis that is different than the second axis and the first axis. In one embodiment, the third axis is offset about 60 degrees relative to the second axis. The plurality of prism arrays can be disposed on a top surface of the light guide.

[0005] An optical microstructure is also provided which includes a plurality of tilted prism arrays that periodically alternate orientation of the tilted prism arrays along a first axis. The prism arrays can also periodically alternate orientation along a second axis and, in alternative embodiments, along a third axis. The optical microstructure can be disposed on a first surface of a film. A plurality of prism arrays can be disposed on a second surface of the film. The plurality of prism arrays on the second surface can be tilted and periodically alternate orientation along at least one axis. The purpose of the periodic alternate orientation of the prism angles is to create alternating bands of bright and dark lines which can be seen viewing the surface of the luminaire. Very small or fine pitch prisms that are not visible to the human eye beyond 0.5 meters can be made to look like macro prisms because of the visibility of the bright and dark bands. Low cost manufacturing concepts, such as continuous casting, can be used to form the precision fine pitch alternating prism groups and achieve the appearance of a precision macro prism, for example, 0.508 to 2.54 mm (0.02 to 0.1 inch) pitch, which would normally be made with a more expensive manufacturing concept, such as compression molding.

[0006] Multi-faceted prisms can be used, for example, prisms that have more than one slope on a facet. Further, prisms can be used which have curved facets or curved prisms tips and valleys. These features are used to smooth the resulting light distribution.

[0007] A method for redirecting light is also provided which includes providing a light source, receiving light radiating from the light source in a light guide, and redirecting the light in a first direction with a plurality of tilted prism arrays that periodically alternate orientation along a first axis. The plurality of tilted prism arrays can periodically alternate orientation along a second axis different than the first axis. The plurality of tilted prism arrays can further periodically alternate orientation along a third axis which is different than the second axis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

[0009]FIG. 1 is a partial cross-sectional view of a waveguide for use in a display apparatus particularly illustrating linear prisms arranged in accordance with the present invention.

[0010]FIG. 2 is a cross-sectional view of a luminaire employing waveguide of FIG. 1.

[0011]FIG. 3 is a cross-sectional view of a pair of waveguides which receive and direct light from a light source substantially downward.

[0012]FIG. 4 is a graph illustrating light output of an exemplary backlit display apparatus at an observation or viewing angle range of about −90° to +90°.

[0013]FIG. 5 are graphs illustrating light output of an exemplary backlit display apparatus at viewing range of about −70° to +70°.

[0014]FIG. 6 is a cross-sectional view of an alternative embodiment of a luminaire in accordance with the present invention.

[0015]FIG. 7 illustrates photometric data from the luminaire of FIG. 6.

[0016]FIG. 8 is a cross-sectional view of another embodiment of a luminaire in accordance with the present invention.

[0017]FIG. 9 is a cross-sectional view of yet another embodiment of a luminaire in accordance with the present invention.

[0018]FIG. 10 is a cross-sectional view taken along line 10-10 of FIG. 6.

[0019]FIG. 11 is an enlarged view of the prisms shown in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0020] A description of preferred embodiments of the invention follows. Generally, the invention is directed to a backlit display apparatus (“BLDA”) having a coarse appearance. An example of a BLDA is disclosed in U.S. Pat. No. 5,629,784, issued to Abileah et al. on May 13, 1997, the teachings of which are incorporated herein in its entirety by reference.

[0021]FIG. 1 is a partial cross-sectional view of a waveguide or light guide 10 for use in a BLDA particularly illustrating the linear prisms 12. The prism angles, in one embodiment, are 25°−90°−65° (90° is the peak angle with a first side of the prism is 25° from the horizontal to peak and a second side of the prism is 65° from the horizontal to the peak). The pitch, or tip to tip spacing, in one embodiment, is in the range from about 0.0508 to 0.254 mm (0.002 to 0.01 inches). The tilting angle, as measured from the peak angle, can be in the range between about 20 and 70 degrees. The prism arrays preferably alternate or flip-flop in orientation, i.e., they are mirror images with respect to line L. In one embodiment, the prism arrays flip-flop every few millimeters, for example, one to two millimeters.

[0022] The waveguide 10 can be solid being formed from a material such as polymethyl methacrylate (PMMA) or other suitable materials. In alternative embodiments, any of the prisms disclosed herein can be used with hollow waveguides in any of the embodiments as disclosed in U.S. application Ser. No. 09/725,338, Attorney's Docket No. 1571.1140-001, filed on even date herewith, the contents of which are incorporated herein by reference.

[0023] When viewed from below, one set of fine pitch prisms 12 is generally oriented to reflect light towards the viewer, and the neighboring pair away from the viewer. Thus, the viewer sees a set of alternating bright and dark lines, which can be referred to as a coarse appearance. It is understood that the number of prisms 12 within a prism grouping is variable, which means that the width of a group and its coarseness can be easily controlled.

[0024]FIG. 2 illustrates a luminaire 8 having an exemplary waveguide 10 coupled to a light source 14, such as a fluorescent cylindrical bulb. A viewer at point X sees the center group of prisms 12 as brighter because they direct light from the source 14 to point X. Since the light from adjacent prism groups is directed elsewhere, these groups appear dark. At point Y, the center group can appear dark, and the adjacent groups are brighter. At some point between X and Y, the groups appear to be equal in brightness.

[0025] Further, the output light distribution is such that the image of the light source 14, such as a cylindrical bulb, is masked. It is noted that the prisms 12 of FIG. 2 are substantially enlarged for illustrative purposes only.

[0026]FIG. 3 illustrates a luminaire 9 having a pair of waveguides 10 which receive and direct light from source 14 substantially downward. A reflective coating 16, such as vacuum metalized aluminum or metalized polyester (PET) or polished aluminum, is provided on the top and end surfaces of the waveguide 10 to allow the light rays to be directed substantially downward.

[0027]FIG. 4 is a graph illustrating light output (luminance: y axis) of an exemplary BLDA at an observation or viewing angle range of about −90° to +90° (x axis). The coarseness or banding appears in this embodiment from approximately −45° to +45°. In this embodiment, the pitch, or tip to tip spacing, is in the range from about 0.0508 to 0.254 mm (0.002 to 0.01 inches).

[0028]FIG. 5 are graphs illustrating light output (lux: y axis) of an exemplary BLDA at viewing angle range of about −70° to +70° from normal (x axis). One graph illustrates the light output across the light source or bulb while the second graph illustrates the light output with the bulb. The data for the graphs are shown in FIG. 5.

[0029]FIG. 6 illustrates an alternative embodiment of a luminaire 11 having an exemplary waveguide 10′ and prisms 12′ wherein the waveguide and prisms are formed separately and laminated together, for example, with a pressure sensitive adhesive (PSA). The waveguide 10′ and prisms 12′ can be formed from different materials. In one embodiment, the prisms 12′ can be formed from an ultraviolet (UV) curable acrylate thermoset or other suitable materials. Either the waveguide 10′ or the prisms 12′ (or both) can be colored and/or have printed patterns formed thereon (e.g., logos) to customize the appearance of the luminaire as disclosed in U.S. application Ser. Nos. 09/013,696, now U.S. Pat. No. 6,119,751, and 09/170,014, now U.S. Pat. No. 6,120,636, filed Jan. 26, 1998 and Oct. 13, 1998, respectively, the teachings of each being incorporated herein in their entirety by reference.

[0030]FIG. 7 illustrates photometric data from a light system, such as shown in FIG. 6. The photodetector was placed about 1.0 meter from the light source. The data represents theoretical and actual measurements taken across the bulb direction, i.e., in the direction of the two-headed arrow 18 of FIG. 6.

[0031]FIG. 8 illustrates another embodiment of a luminaire 19 having mirrors 20 positioned on the ends of the waveguide 10 and above and below the light source 14. The prisms 12′ can be integral to the waveguide 10, or alternatively, be laminated to the waveguide 10.

[0032]FIG. 9 illustrates a luminaire 22 which is similar to the embodiment of FIG. 8 but instead of a mirror above the light source 14, a baffle 24 is provided there instead. The baffle 24 can include a white surface which absorbs, diffracts, and scatters light from the light source 14. It is believed that this baffle 24 more uniformly directs the light rays into the waveguide 10 for achieving a more uniform distribution of the light rays in the waveguide.

[0033] The table below compares the viewing angle, the measured luminance for the luminaire 19 of FIG. 8 and theoretical output for a luminaire having a baffle such as the luminaire 22 of FIG. 9. In this embodiment, the pitch of the prisms is about 0.254 mm (0.01 inches). Measured Luminance Angle (cd/lux/m²) Theoretical with Baffle 180 5.7 16.8458 185 5.1 18.9760 190 5.1 15.2260 195 5.3 8.9539 200 7.6 15.5152 205 13.8 27.0215 210 19.9 37.7291 215 28.2 33.6113 220 37.0 37.6789 225 44.7 44.4249 230 48.9 40.6028 235 47.4 41.2673 240 39.3 35.1872 245 26.1 24.0277 250 10.9 10.6000 255 4.9 4.7000 260 4.6 4.5000 265 4.3 4.2000 270 1.7 1.6000 275 2.8 2.7000 280 5.5 5.4000 285 9.5 8.8104 290 13.0 10.9029 295 15.5 5.3704 300 17.0 8.9190 305 18.7 5.3252 310 21.7 13.4086 315 26.2 18.7654 320 31.8 22.4112 355 38.3 32.3889 330 45.6 43.3254 335 54.5 45.7689 340 53.0 56.6042 345 45.1 49.3210 350 33.0 45.7512 355 21.8 47.1792 0 17.4 41.8723 5 20.2 54.5000 10 30.4 48.0831 15 41.6 46.7072 20 49.6 45.5090 25 5136 47.0374 30 44.0 38.3052 35 36.0 32.6696 40 29.2 21.6011 45 23.8 19.2380 50 19.2 11.7001 55 15.7 6.5985 60 13.4 4.6328 65 12.0 7.7141 70 10.0 9.9115 75 7.5 7.4000 80 7.4 7.3000 85 3.1 3.0000 90 1.9 1.8000 95 3.4 3.3000 100 3.7 3.6000 105 4.0 3.9000 110 7.2 7.1000 115 21.5 21.4000 120 37.2 35.3846 125 46.5 42.8789 130 49.7 45.9643 135 46.7 45.6916 140 38.6 38.2638 145 29.6 36.6630 150 21.1 33.6147 155 14.3 32.8648 160 8.2 13.3652 165 5.5 10.2196 170 5.1 15.5559 175 5.3 18.9760

[0034] The linear prisms 12 as described above can be referred to as a one-dimensional structure. That is, the prism structures 12 have peaks and valleys running along one

[0035] axis. In alternative embodiments, the prisms 12 can include multiple-dimensional structures, such as two-dimensional structures and three-dimensional structures.

[0036] For example, in the embodiment of FIG. 6, a two-dimensional prism structure can be constructed by forming a second array of linear prisms perpendicular to the linear prisms 12′. More particularly, a row of linear prisms having peaks 26 and valleys 28 is formed perpendicular to the longitudinal axis of the existing linear prisms 12′, i.e., into the paper. Thus, a cross-sectional view taken along line 10-10 is seen in FIG. 10. If the prisms are spaced apart, the peaks 26 will have a flat portion as also illustrated in FIG. 10. FIG. 11 illustrates an enlarged view of the prisms of FIG. 6 which illustrates peaks 26 and valleys 28 of the prism arrays. This facilitates controlling of the light rays exiting the waveguide at every angle. In alternative embodiments, the peaks and valleys can be offset at about 60 degree intervals to provide a three-dimensional structure. In further embodiments, the peaks and valleys can be offset at various angles to provide a multiple-dimensional structure.

[0037] In alternative embodiments, optical microstructures can be formed on, laminated to, or otherwise provided on sheets, panels, or films for use in luminaires in which control of light distribution is desired. Furthermore, each side of the sheet, panel, or film can have an optical microstructure thereon. These optical microstructures can have tilted prism arrays which alternate orientation along one or more axes.

[0038] In any of the disclosed embodiments, multi-faceted prisms can be used, for example, prisms that have more than one slope on a facet. Further, prisms can be used which have curved facets or curved prisms tips and valleys. These features can be used to smooth the resulting light distribution.

[0039] While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. 

What is claimed is:
 1. An optical microstructure comprising a plurality of tilted prism arrays that periodically alternate orientation of the tilted prism arrays along a first axis.
 2. The optical microstructure of claim 1 wherein the prism arrays periodically alternate orientation of the tilted prism arrays along a second axis.
 3. The optical microstructure of claim 1 wherein the prism arrays periodically alternate orientation of the tilted prism arrays along a third axis.
 4. The optical microstructure of claim 1 wherein the optical microstructure is disposed on first surface of a film, further comprising a plurality of prism arrays on a second surface of the film.
 5. The optical microstructure of claim 4 wherein the plurality of prism arrays on the second surface are tilted and periodically alternate orientation along at least one axis.
 6. The luminaire of claim 1 wherein the prism arrays include prism facets having more than one plane on at least one facet. 